This invention relates generally to electrographic transfer apparatus, and more particularly to a drive mechanism for an electrographic transfer roller apparatus.
In the operation of a typical electrographic reproduction apparatus, a dielectric member, such as a rotatable drum or movable web, is transported about a continuous path into operative relation with electrographic process stations to make information reproductions. During the reproduction process carried out at such process stations of the reproduction apparatus, the dielectric member is uniformly charged and then exposed to an image of information to be reproduced (e.g., reflected light image of a document or electrostatically formed image) to form an electrostatic charge pattern on the member corresponding image-wise to such information. The charge pattern is developed, for example, with pigmented thermoplastic marking particles electrostatically attracted to the charge pattern to form a transferable image on the dielectric member. The transferable image is then transferred from the dielectric member to a receiver member, such as a cut sheet of plain bond paper for example, to form the information reproduction, and the dielectric member is cleaned for reuse.
One technique used to transfer the transferable image from the dielectric member to the receiver member is to transport the receiver member along a path between the dielectric member and a roller urged into contact with the dielectric member. An electrical potential is applied to the roller and establishes an electrostatic field between the roller and the dielectric member. The electrostatic field causes the marking particles of the transferable image to be attracted to the receiver member, the particles adhering to the receiver member as the member leaves the dielectric member. Generally, the transport of the receiver member during transfer is accomplished by attaching the receiver member to the roller upstream of the transfer zone, and rotatably driving the roller to feed the attached receiver member through such zone.
Drive for the transfer roller is positively related to drive for the dielectric transfer member to enable the receiver member, attached to the roller, to be registered relative to transferable image on the dielectric member and to move the roller and dielectric member at the same peripheral speed through the transfer zone. However, the peripheral speed of the surface of the receiver member attached to the roller is slightly greater than the peripheral speed of the roller. Thus different thicknesses in receiver members result in different member peripheral surface speeds. Therefore, matching of the peripheral surface speed of the receiver member and the peripheral speed of the dielectric member is difficult to achieve; and, a mismatch in such peripheral speeds may cause degradation of the transferred image such as by smearing of the image. Such image degradation is, of course, amplified when a plurality of transferable images are transferred to a receiver member as when making multicolor reproductions. Furthermore, any nonuniformities in the positive drive relation will disturb the transfer process which also causes defects in the transferred image.